Nowadays, low-power circuit design has become more and more attractive due to an energy revolution. Many energy-saving technologies, such as the low voltage technology, dynamic voltage switching, subthreshold operating region design and so forth, have been proposed.
Moreover, energy harvesting also plays an important role in the environment. Energy harvesting has the potential to replace batteries for small and low-power electronic devices. That is to say, the energy harvesting technology is able to provide a very small amount of power for low-energy electronics. This has several benefits, such as maintenance free, environmentally friendly and opening up new application.
Further, energy harvesting devices may convert ambient energy into electrical energy, and have attracted much interest in the commercial sector. Some energy harvesting systems convert motion into electricity to be used by oceanographic monitoring sensors for autonomous operation. Future applications are in wearable electronics, where energy harvesting devices can recharge or power cellphones, mobile computers, radio communication equipment, etc. All of these devices must be sufficiently robust to endure long-term exposure to hostile environments.
As such, for the sake of meeting the requirements of the small chip area, low cost and extraordinarily low power, it is necessary to design an integrated miniaturize circuit capable of providing extremely low power in terms of the cost effectiveness, uncomplicated structure, compact design and versatility when used with relatively low supply voltages.